In general, a conventional transmission line connecting structure is known wherein a slot line is configured by forming a slot of a predetermined slot width dividing a front surface electrode formed on the front surface of a dielectric substrate, for example, and multiple such slot lines are connected to each other (e.g., see Patent Document 1). With such conventional art, the front face electrodes of two slot lines are positioned in a state opposing one another across a predetermined gap provided therebetween, and also provided to each front surface electrode is a slot resonator with one end open which is made of a generally square notch wherein the edge on the gap side is open. The slot lines are each connected to each slot resonator, and also these two slot resonators are coupled one to another, with the two slot lines being connected so as to be capable of propagating high-frequency signals. Also, a configuration of a transmission/reception device is known, such as a communication device using such a transmission line connecting structure (e.g., see Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-308601
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-101301
With the conventional art in Patent Document 1, one end of the slot resonators are open towards the gap between the two front surface electrodes, and so the high-frequency signal can leak from the open edge sides of the slot resonators towards the gap. When a transmission/reception device using a transmission line is housed within a package as described in Patent Document 2, in general the front surface electrode is in contact with a conducting wall face in the package and is grounded for example. Accordingly, the front end of the gap is short-circuited by the wall face within the package. In other words, the gap between the front surface electrodes function as a leakage line, and also the front edge of this leakage line is short-circuited by the package. Thus, the actual current from the leaked high-frequency signal flows at the short edge (short-circuit edge) of the leakage line in the package, and so the resonance frequency of the slot resonator can easily be influenced by the connection state of the front surface electrode and the package. As a result, a problem can occur wherein the coupling properties of the two slot lines become unstable.
Also, the resonance frequency of the slot resonators changes based on the distance from the slot resonator to the package. Thus, in order to maintain the coupling properties between the slot lines constant, the measurement precision of the parts of the dielectric substrate, the front surface electrode, and the package and the like, and the mounting precision when mounting the dielectric substrate within the package, needs to be improved. Thus, a problem can occur wherein the manufacturing cost for configuring a module such as a communication device increases.
Further, the resonance frequency of the slot resonators changes according to the distance measurements of the leakage line between the package and the slot resonator, and so the connecting structure of the package and the front surface electrode needs to be designed for each measurement of the package. Thus, there is the problem of low design freedom.